1. Field of the Invention
The present invention relates to a liquid ejection head that employs a scheme in which liquid is ejected by using energy, and a method of manufacturing the liquid ejection head.
2. Description of the Related Art
Through similar processes to that for semiconductor manufacturing, a substrate for a liquid ejection head is manufactured by forming, on the same substrate, multiple heaters for heating liquid to generate bubbles when being energized, lines for providing electrical connection to the heaters, and the like. Then, a liquid ejection head is constructed in a way that a member (nozzle formation member) forming ejection openings and liquid passages is provided on the substrate. Here, the ejection openings are provided corresponding to the heaters and are used to eject ink therefrom. Meanwhile, the liquid passages are formed to communicate with the corresponding ejection openings, respectively.
One method of manufacturing the liquid ejection head (see Japanese Patent Laid-Open No. H06-286149 (1994) includes the following steps:                (1) forming a pattern to form the liquid passages on the substrate with a dissolvable resin;        (2) applying a coating resin containing an epoxy resin being solid at ordinary temperature;        (3) forming openings to be the ejection openings in the coated resin; and        (4) dissolving the dissolvable resin layer.        
Further, there has been proposed a liquid ejection head and a method of manufacturing a liquid ejection head in which a layer made of a polyetheramide resin (called an adhesion improvement layer below) is interposed between the substrate and the nozzle formation member in order to improve the adhesion between them (see Japanese Patent Laid-Open No. H11-348290 (1999)).
FIG. 8A is a schematic perspective view showing a general example of the configuration of the liquid ejection head, and FIG. 8B is a cross-sectional view taken along the VIIIB-VIIIB line in FIG. 8A. A substrate 1110 made of Si or the like is provided with an ink supply opening 1202 being a slot-like through-hole, and ink is introduced into this ink supply opening 1202. Further, two arrays of heaters 1214 are formed, one on each side of the ink supply port 1202. Electrode portions 202 are formed along a side of the substrate 1110 in a direction perpendicular to an arrangement direction of the heaters 1214. The electrode portions 202 are formed to provide external electric connection to the heaters 1214 or to a logic circuit for selectively energizing the heaters 1214, and are connected to the heaters 1214 or to the logic circuit via lines 201. Then, a nozzle formation member 203 is disposed on the substrate 1110 in a contacting manner. The nozzle formation member 203 is provided with liquid passages 1106 and ejection openings 1107 from each of which ink is ejected toward a printing medium with the action of thermal energy.
To reduce a line resistance value, the following technique has been proposed. Specifically, the lines 201 and the electrode portions 202 are simultaneously formed as a gold (Au) layer by plating (see Japanese Patent Laid-Open No. 2005-199701). Gold has excellent properties as a line material because of its low electric resistance, high chemical stability, high electromigration characteristics, and the like. Particularly, gold is excellent as a line material of a substrate for a liquid ejection head because the lines constantly exist very close to the ink being liquid and are used to energize the heaters to raise their temperature instantly.
Regarding the above lines, there is a need to form an upper layer on the lines in cases as follows.
In the configuration of the liquid ejection head described in Japanese Patent Laid-Open No. H06-286149 (1994) or No. H11-348290 (1999), a surface of metal such as the lines existing on the substrate adheres to an organic resin constituting the nozzle formation member or the adhesion improvement layer. This adhesion is thought to be brought by a physical anchor effect of the organic resin entering the dips in the surface of the metal, and also by chemical bond, hydrogen bond, or the like through the OH groups existing on the surface of the metal.
However, depending on the line material, the following problems may arise. For example, in a case where lines are formed of gold, as gold is a stable noble metal and has a few OH groups on its surface, gold has poor bonding power with an organic resin. In addition, on a liquid ejection head substrate, the organic resin film swells because ink constantly exists near the ejection openings. Particularly, in a liquid ejection head substrate with heaters, heat generated by the heaters causes the organic resin and the substrate to expand to different degrees. As a result, the liquid ejection head substrate with heaters undergoes internal stress caused by the difference in thermal expansion between the substrate and the organic resin, in addition to the swelling of the organic resin film. This stress could possibly cause separation of the nozzle formation member from the Au layer, originating from and around parts having poor adhesion with the organic resin. To avoid such a separation, an upper layer may be required on the lines. Besides this, an upper layer may be formed for other various objectives. For example, an upper layer may be required on a desired portion of lines in order to improve the reliability by protecting a line surface and the like from damages.
A possible way to form the upper layer is to form and then pattern a film of an insulating material, such as SiN or SiC by using a vacuum film forming device or the like, on and in the vicinity of the lines. However, since the vacuum film forming device and a patterning device are expensive, the above way will result in increased costs for manufacturing the substrate, and in turn, the liquid ejection head. In addition, there is concern that the manufacturing process of the substrate becomes complex. Moreover, the above way may possibly lower the energy efficiency in a liquid ejection head that employs the scheme in which liquid is ejected by using energy generated by the heaters.